1. Field of the Invention
This invention relates to a hyperthermia apparatus or in other words a unit which generates high-frequency power for treating an affected area of a patient's body by producing a local elevation of temperature. The distinctive feature of the invention lies in the fact that it permits deep hyperthermia.
2. Description of the Prior Art
It is known that certain ailments can be treated by inducing a temperature rise of a few degrees in the affected region. For example, gonococcal infections can be treated in this manner since gonococci are totally destroyed at a temperature between 41.degree. and 42.degree.. This method is also very promising for the resorption of certain tumors, in particular by reason of the fact that they are irrigated to a lesser degree than adjacent healthy tissues and therefore less efficiently cooled, with the result that their temperature rises to higher levels than in healthy tissues when they are subjected to the action of microwaves.
In hyperthermia units of the type used experimentally up to the present time, two electrodes are placed on each side of the region to be heated (for example a dorsal electrode and a ventral electrode). These electrodes are connected to a high-frequency generator having a medium power rating (a few tens of watts) which operates at a frequency of the order of 1 MHz or 10 MHz. In order to comply with current standards, a frequency of 13.56 MHz is often adopted.
However, a system of this type is subject to serious drawbacks since the distribution of high-frequency energy dissipated within the volume delimited by the two electrodes is not uniform. The curve of distribution between the two electrodes has substantially the shape of a bowl. In other words, a higher temperature rise is observed in the immediate vicinity of the two electrodes, the temperature-rise ratio between the adjacent zones of the electrodes and the center of the interelectrode space being of the order of 2 to 3. This is attended by two disadvantages. In the first place, the effectiveness of the treatment is reduced when the affected region is located at an appreciable depth. Secondly, there is a potential danger of burning in areas close to the skin. An attempt has been made to solve this problem by interposing between the electrodes and the patient a predetermined volume of water trapped within a flexible envelope provided with an inlet and an outlet so as to permit circulation and therefore surface cooling. Under these conditions, the temperature distribution curve exhibits a falloff in the vicinity of the electrodes but this produces only a slight improvement in deep treatment. It is in fact hardly possible to increase the high-frequency power since cooling remains effective to a depth corresponding to only the first few millimeters of tissue for reasons of thermal conductivity.